1. Field of the Invention
This invention relates to polyalphaolefins. Specifically, the invention relates to controlling the branch level and viscosity of polyalphaolefins.
2. Discussion of the Background Information
Catalytic oligomerization of olefins is a known technique for manufacturing hydrocarbon basestocks useful as lubricants. Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for several decades, leading to recent commercial production of a number of superior polyalphaolefin synthetic lubricants (hereinafter referred to as “PAO”). These materials are primarily based on the oligomerization of alphaolefins such as C6-C12 olefins. Industrial research effort on synthetic lubricants has generally focused on fluids exhibiting useful viscosities over a wide range of temperatures, i.e., improved viscosity index (VI), while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. These newer synthetic lubricants provide lower friction and hence increase mechanical efficiency across the full spectrum of mechanical loads and do so over a wider range of operating conditions than mineral oil lubricants.
Well known structural and physical property relationships for high polymers have pointed the way to alphaolefins as a fruitful field of investigation for the synthesis of oligomers with the structure believed to be necessary to confer improved lubricant properties thereon. Due largely to studies on the polymerization of propene and vinyl monomers, the mechanism of the polymerization of alphaolefins and the effect of that mechanism on polymer structure is reasonably well understood, providing a strong resource for targeting on potentially useful oligomerization methods and oligomer structures. Building on that resource, oligomers of alphaolefins from 6 to 12 carbon atoms have been prepared with commercially useful synthetic lubricants from, e.g., 1-decene oligomerization, yielding a distinctly superior lubricant product via either cationic or Ziegler catalyzed polymerization.
A significant problem in the manufacture of synthetic lubricants is the production of lubricants in a preferred high kinematic viscosity range with good low temperature viscosity characteristics, in good yield, and without excessive catalyst residue. Methods to control the viscosity index are sought after in the art to overcome the problems in the manufacture of, particularly, lower viscosity lubricants.